Morphological variation of the unionidae mussel Anodonta anatina

Abstract

ABSTRACT

Morphology of a given species can vary among individuals, morphology differences can be found between populations males can be different from females (sexual dimorphism) or e.g. with young and old individuals. The aim of the present study was to investigate morphological variability in the unionidae mussel Anodonta anatina originating from two populations. Measured variables included length, height, width, volume and dry mass of shell, dry mass of soft tissues and gill blades, and age, sex, estimation of glochidium larvae produced. The main results included faster growth of mussels in Lake Koijärvi than in Lake Päijänne (at the age of 4-5 years), which may reflect the higher productivity in Lake Koijärvi—and also faster growth of females in Lake Koijärvi (at the age of 4 years). In addition, shell was relatively higher in small individuals and in males than in bigger mussels or females. On the other hand, shell of big mussels (in Lake Koijärvi) and females was relatively wider in shape, and the shell volume was higher in females than in males. This sexual dimorphism could be due to space requirements of the glochidium larvae developed in female gills. The total dry mass of soft tissues (in both populations), as well as the mass of gill blades (in Lake Päijänne), was higher in females than among males, but the mass of body without gills was higher in males (in Lake Päijänne). The mass of shell compared to mass of soft parts did not differ between sexes in Koijärvi but in big-sized Päijänne mussels the males had heavier shells than females. These results indicate clear sexual dimorphism and population-dependent differences in morphology of A. anatina.